How Is a Glaucoma Test Performed?

A glaucoma test is a comprehensive eye examination that assesses intraocular pressure and the condition of the optic nerve together, either to diagnose glaucoma or to monitor a suspected case. It is not a single measurement: intraocular pressure, the structure of the optic disc, corneal thickness and, when needed, the visual field are all assessed together.

This combined approach distinguishes people with raised pressure but no optic nerve damage yet from patients with an actual diagnosis of glaucoma.

Because glaucoma usually progresses without obvious symptoms, the test aims not only to explain an existing complaint but to catch unnoticed damage at an early stage. It is therefore recommended both for people with a specific complaint and for symptom-free people at risk.

At our clinic in Istanbul, the examination is tailored by Op. Dr. Anıl Kaya to the patient's age, risk factors and any previous records.

A glaucoma test is usually completed within 20 to 30 minutes; if the pupils need dilating for fundus or optic nerve imaging, it can take longer. Tonometry, a biomicroscopic optic nerve exam and, when required, OCT imaging and a visual field test are standard steps. Most tests do not typically cause discomfort; dilating drops can leave vision temporarily blurred for a few hours.

A glaucoma test assesses three main elements: intraocular pressure, measured with tonometry; the structure of the optic disc and nerve fibre layer, examined with a biomicroscope and OCT; and, where necessary, the visual field, measured with perimetry. Corneal thickness is also recorded so the pressure reading can be interpreted correctly, since a thin or thick cornea can make the measured value differ from the true pressure.

In some patients, gonioscopy may be added to view the drainage angle directly, helping distinguish open-angle from angle-closure glaucoma. None of these measurements is sufficient alone — what matters is assessing the findings together.

A glaucoma test is particularly recommended for people over 40, those with a family history of glaucoma, high myopia, a systemic condition such as diabetes or high blood pressure, and anyone with a previous eye injury. In these risk groups, because glaucoma can progress without symptoms, regular intraocular pressure checks matter. People with no complaints but in a risk group are also advised to have periodic eye examinations.

Recommended frequency depends on age, family history and earlier findings such as intraocular pressure; the intervals below are general guidance, and the exact frequency is set by the doctor after examination.

Noticing a narrowing of your visual field, difficulty seeing objects at the edges, marked difficulty with night vision, or a tunnel-like sensation are among the symptoms that call for a glaucoma test. More on the possible causes of this complaint, and when to take it seriously, is on our peripheral vision loss page.

Sudden severe eye pain, nausea, halos around lights or sudden redness point to a different level of urgency and can be associated with angle-closure glaucoma; these should be assessed without delay.

However, most glaucoma progresses without symptoms, so regular examination is recommended for risk groups even without a complaint.

During the examination, intraocular pressure is measured first with a tonometer. The front of the eye and optic disc are then assessed with a biomicroscope; if needed, OCT measures the nerve fibre layer thickness, important for detecting early-stage damage. Corneal thickness is recorded with pachymetry.

In suspected or diagnosed cases, peripheral vision is assessed with a visual field test (perimetry). None of these tests is expected to cause pain, and most are completed in one visit; some may require dilating drops.

The steps below summarise the general flow; which are used, and in what order, can vary by patient.

1. 1Intraocular Pressure Measurement. An initial assessment is made by measuring intraocular pressure with a tonometer.
2. 2Anterior Segment and Optic Nerve Examination. The front of the eye and the appearance of the optic disc are examined with a biomicroscope.
3. 3Corneal Thickness Measurement. Corneal thickness, measured by pachymetry, helps with the correct interpretation of the pressure reading.
4. 4Optic Nerve Fibre Imaging. OCT (optical coherence tomography) examines the thickness of the nerve fibre layer at micron level.
5. 5Visual Field Test If Needed. In suspected or diagnosed cases, peripheral vision is assessed with a perimetry test.

Intraocular pressure above normal does not, alone, confirm glaucoma; what matters is whether there is structural optic nerve damage and/or a corresponding visual field loss. If pressure is high but the nerve and visual field are normal, this is monitored as raised eye pressure or suspected glaucoma.

If optic nerve damage is found with a corresponding visual field loss, glaucoma is diagnosed and staged (early, moderate or advanced). Results are interpreted against previous records, since change over time matters more in glaucoma monitoring than a single measurement.

For patients followed as suspected glaucoma, the aim is a regular follow-up plan that catches change early, not waiting for damage to occur; a suspicious finding is a reason for monitoring, not concern.

The most important condition a glaucoma test detects is glaucoma itself; findings help determine its stage and the appropriate treatment step. Sometimes, before a diagnosis is confirmed, only a raised intraocular pressure is found — an intermediate picture called suspected glaucoma or raised eye pressure — and the patient is monitored at set intervals. General information about glaucoma, its course and risk factors is on our glaucoma page.

Findings unrelated to glaucoma may also be noticed: early lens clouding (cataract), a retinal finding worth attention, or an uncorrected refractive error. If found, you can look into the relevant subject on our cataract, retina or laser eye surgery pages, and book a separate appointment if needed.

The grouping below reflects a general tendency, not an exact proportion; the definite diagnosis is made through the doctor's assessment.

If glaucoma is diagnosed, or suspected glaucoma is confirmed, a treatment plan is built to bring intraocular pressure to a target level. It can start with drops and progress step by step to laser or surgery if needed. Detailed treatment information is on our glaucoma treatment page.

When drops give an insufficient response, or are unsuitable, laser options are considered; when medication and laser are not enough, or the disease has advanced, surgery is considered instead. The appropriate step depends on the pressure level, the degree of optic nerve damage and the rate of progression.

If a cosmetic eyelid finding is noticed, the patient may be referred separately for an eyelid surgery assessment, a process separate from glaucoma treatment.

Main tests used in a glaucoma test: tonometry (intraocular pressure), pachymetry (corneal thickness), a biomicroscopic optic nerve exam, OCT for nerve fibre layer (RNFL) analysis, and perimetry (visual field testing). Because OCT-based RNFL analysis can detect subtle optic nerve changes early, it is widely used in glaucoma monitoring.

In suspected cases, gonioscopy may also be used to view the drainage angle directly, helping distinguish open-angle from angle-closure glaucoma. Which test is used depends on the patient's risk level, as determined by the doctor.

If you think you may be at risk for glaucoma, or want a routine eye examination, you can book an appointment with Op. Dr. Anıl Kaya in Istanbul through our contact page.